Growth stages booklet pages 18-19

Flag Leaf

The flag leaf is the last leaf to emerge before the head. It begins to emerge just after the third above-ground node is observed on most varieties (Fig. 36-37). The flag leaf contributes 75 percent or more of the photosynthate needed for maximum grain yield. Flag leaf emergence is a visual indicator that the plant will soon be in the boot stage.
Fig. 36 The flag leaf of a wheat plant.	Fig. 37. Dissected flag-leaf wheat plant with seven leaves, three tillers and two detectable nodes.

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Boot Swollen

Following flag leaf development, flag leaf sheath and the peduncle elongate and the developing head is pushed up through the flag leaf sheath. The leaf sheath swells to form the boot as the head continues to develop (Fig. 38). The boot stage is complete when the awns (or the head in awnless varieties) become visible at the flag leaf collar and the sheath is forced open by the developing head.	Fig. 38. The boot of a wheat plant.

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Head Emergence And Flowering

Heading occurs as the peduncle continues elongation and pushes the head out of the flag leaf collar (Fig. 39-41). Flowering (pollination) may occur either before or after head emergence depending on plant species and variety. Pollen formation and pollination are very sensitive to environmental conditions. Cereals are classified as either open-flowering or closed-flowering types. Flowering usually occurs in close-flowering varieties prior to head emergence and in open-flowering varieties shortly after head emergence. Many winter barley varieties are open-flowering whereas spring barley varieties are usually closed-flowering. Most varieties of wheat are of the open-flowering type. Flowering in open varieties is usually observed by anther extrusion from each floret, although this may not occur under stress conditions. In closed-flowering types, the anthers remain inside each floret. If the anthers within a floret are yellow or gray rather than green, it is reasonably certain that flowering has occurred (Fig. 42-43). Generally, flowering in wheat begins within three or four days after head emergence, while flowering in barley usually occurs just before or during head emergence. Flowering begins from about the middle section of the main stem head and progresses to the top and bottom of the head. All heads of a plant flower within a few days. Within a few hours of pollination, the embryo and endosperm begin to form.

Fig. 39. A wheat plant with head emerged. (Z=57,F=10.4, H=10.7)	Fig. 40. A barley plant with head emerged. (Z=50, F=10.1, H=10.2)

Fig. 41. Dissected wheat plant with seven leaves, two tillers, and three detectable nodes.	Fig. 42. A magnified wheat floret before flowering.
	Fig. 43. A wheat head after anthesis.

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